Reland "[bazel] Fix golang cross-compilation on RBE"

This is a reland of commit b2109e6

See cr/488438081

Original change's description:
> [bazel] Fix golang cross-compilation on RBE
>
> Without this change, one could not have a Mac Bazel host
> and use our Linux executor to build for a Mac target.
> What I observed was the host uploading the Mac go toolchain
> to the Linux RBE instance and that not working.
>
> To fix this, we explicitly download a Linux golang toolchain
> as well as one for the host machine. This is straightforward
> after the fact (See WORKSPACE.bazel) but took a bit of
> experimentation and doc reading to get right.
>
> To *use* the right toolchain, one must tell the Linux
> RBE instance the target platform should be the same as
> the host platform. This is a smidge tricky to do correctly
> in a script (e.g. a Makefile), so I also added a short
> Bazel (read: Python) script to call `go version` and parse
> the output into a Bazel-ready os_arch string.
>
> Change-Id: If009316209c46efa912f39f0f55bd7d6734d27c5
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/604061
> Reviewed-by: Leandro Lovisolo <[email protected]>

Change-Id: I8bbeee8bbf6109810915125d581548ebc36acff0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/605077
Reviewed-by: Leandro Lovisolo <[email protected]>

PRESUBMIT.py

@@ -252,7 +252,7 @@ def _CheckBazelBUILDFiles(input_api, output_api):
     excluded_paths = ["infra/", "bazel/rbe/", "bazel/external/", "bazel/common_config_settings/",
                       "modules/canvaskit/go/", "experimental/", "bazel/platform", "third_party/",
                       "tests/", "resources/", "bazel/deps_parser/", "bazel/exporter_tool/",
-                      "tools/gpu/gl/interface/"]
+                      "tools/gpu/gl/interface/", "bazel/utils/"]
     is_excluded = any(affected_file_path.startswith(n) for n in excluded_paths)
     if is_bazel and not is_excluded:
       with open(affected_file_path, 'r') as file:

WORKSPACE.bazel

@@ -92,10 +92,10 @@ pip_install(
 #######################################################################################
 http_archive(
     name = "io_bazel_rules_go",
-    sha256 = "2b1641428dff9018f9e85c0384f03ec6c10660d935b750e3fa1492a281a53b0f",
+    sha256 = "099a9fb96a376ccbbb7d291ed4ecbdfd42f6bc822ab77ae6f1b5cb9e914e94fa",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.29.0/rules_go-v0.29.0.zip",
-        "https://github.com/bazelbuild/rules_go/releases/download/v0.29.0/rules_go-v0.29.0.zip",
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.35.0/rules_go-v0.35.0.zip",
+        "https://github.com/bazelbuild/rules_go/releases/download/v0.35.0/rules_go-v0.35.0.zip",
     ],
 )
 
@@ -108,7 +108,7 @@ http_archive(
     ],
 )
 
-load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")
+load("@io_bazel_rules_go//go:deps.bzl", "go_download_sdk", "go_register_toolchains", "go_rules_dependencies")
 load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies")
 load("//:go_repositories.bzl", "go_repositories")
 
@@ -117,9 +117,28 @@ go_repositories()
 
 go_rules_dependencies()
 
-go_register_toolchains(version = "1.18")
+# For our Linux RBE pool
+go_download_sdk(
+    name = "go_sdk_linux_amd64",
+    goarch = "amd64",
+    goos = "linux",
+    version = "1.18",
+)
+
+# For the host machine
+go_download_sdk(
+    name = "go_sdk",
+    version = "1.18",
+)
 
-gazelle_dependencies(go_repository_default_config = "//:WORKSPACE.bazel")
+# Do not specify a version here or it will be an error (because we
+# specified the version above when downloading SDKs)
+go_register_toolchains()
+
+gazelle_dependencies(
+    go_repository_default_config = "//:WORKSPACE.bazel",
+    go_sdk = "go_sdk",
+)
 
 # Because the skia infra repo has a dependency on google.golang.org/grpc (aka
 # @org_golang_google_grpc), we need to have this library available to build protos.

bazel/Makefile

@@ -26,7 +26,8 @@ generate_gni:
 .PHONY: generate_gni_rbe
 generate_gni_rbe:
 	cd .. && bazelisk build //bazel/exporter_tool --config=linux_rbe --jobs=100 \
- 			--remote_download_toplevel && \
+ 		--platforms=@io_bazel_rules_go//go/toolchain:$(shell bazelisk run //bazel/utils:go_platform) \
+ 		--remote_download_toplevel && \
         ${EXPORTER_TOOL} -output_format=gni -proj_name=Skia ${EXPORTER_RULES} \
 		&& bazelisk run //bazel/external/gn -- format gn/*.gni modules/*/*.gni
 

bazel/utils/BUILD.bazel

@@ -0,0 +1,38 @@
+# A helper function to get the go platform string of the Bazel host.
+# This can be used to do cross-platform go compilations.
+# Example:
+#    $ bazelisk run //bazel:go_platform
+#    darwin_arm64
+py_binary(
+    name = "go_platform",
+    srcs = ["go_platform.py"],
+    data = ["@go_sdk//:bin/go"],
+    tags = ["no-remote"],  # Need the platform of the host
+)
+
+_GO_PLATFORM = """
+import os
+import subprocess
+
+# https://bazel.build/reference/be/make-variables#predefined_label_variables
+go_exe = os.path.abspath("$(execpath @go_sdk//:bin/go)")
+
+result = subprocess.run([
+    go_exe,
+    "version",
+], capture_output=True, encoding="utf-8")
+
+# e.g. go version go1.18 darwin/arm64
+os_arch = result.stdout.strip().split(" ")[3]
+# e.g. darwin/arm64
+print(os_arch.replace("/", "_"))
+"""
+
+genrule(
+    name = "create_go_platform_script",
+    outs = ["go_platform.py"],
+    cmd = "echo '%s' > $@" % _GO_PLATFORM,
+    exec_tools = [
+        "@go_sdk//:bin/go",
+    ],
+)